1. Field of the Invention
This invention relates to corrosion inhibitors which prevent corrosion of metal surfaces contacted by aqueous compositions containing them. More particularly the invention relates to corrosion inhibitors which are amine salts of mixtures of polycarboxylic acids and boric acid. The invention also relates to aqueous systems containing the aforedescribed corrosion inhibitors and methods of inhibiting corrosion of metal which comprises contacting metal with said aqueous systems.
2. Prior Art
It is known to treat aqueous systems, such as functional fluids (e.g., machining and hydraulic fluids), with corrosion inhibitors to prevent unwanted corrosion of metal surfaces which come in contact with the systems. For example, strongly alkaline systems are used for temporary corrosion inhibition during the production of metal work pieces, during or after cleaning treatments and during machining or at other stages of processing. Typical of the known corrosion inhibitors used in such systems are the alkali metal nitrites and chromium salts. Organic compounds such as alkanol amines, particularly tri-alkanol amines and alkyl or alkanol amine soaps of fatty acids also have been used.
The systems containing nitrites and chromates have the disadvantage that special steps must be taken to prevent their release into waste water without removal of the nitrites or chromates. In addition, certain nitrite-containing materials are suspected carcinogens. Alkanol amines and fatty acid salts have frequently been found to be inadequate corrosion inhibitors requiring the use of excessive levels or supplementary additions of chromate or nitrite. Therefore the need for effective, nonpolluting corrosion inhibitors for aqueous systems has continued.
Efforts to meet this need have resulted in research described in several patents. For example: U.S. Pat. No. 4,113,498 discloses corrosion inhibitors comprising a reaction product of an aliphatic carboxylic acid, a polyhydroxy carboxylic acid and an alkanol amine.
U.S. Pat. No. 4,053,426 and British Patent Specification 1,532,836 describe water-based, metal working fluids containing amine salts of a partial ester of an alkenyl or alkyl succinic acid.
Japanese Patent Application 156,684, as abstracted in Derwent publications abstract number 59567A/33*j5 3079-738, discloses water-soluble corrosion inhibitors for steel containing a carboxylic acid and an amino alcohol.
U.S. Pat. No. 2,726,215 discloses alkali and alkaline earth metal salts of dicarboxylic acids and their use in aqueous systems as corrosion inhibitors.
U.S. Pat. No. 2,638,449 discloses reaction products of fatty acids and dialkanol amines which are further reacted with alkenyl succinic acids having substituents of up to 31 carbon atoms.
U.K. Patent Application 1,521,984, as abstracted in Derwent publications, abstract number J5014W-52, describes detergents made by reacting adipic or sebacic acid with mono-, di- or triethanol amine and adjusting the pH of the reaction product to 7-7.5 with amine. The product is described as being soluble in water.
U.S. Pat. No. 4,120,665 describes water-soluble complex salts of certain metals, hydroxycarboxylic acids and phosphoric esters of alkanol amines and their use as corrosion inhibitors.
U.S. Pat. No. 4,250,042 describes salts of polycarboxylic acids and ammonia. These salts are reported to be useful as metal corrosion inhibitors in aqueous systems and particularly in well-drilling operations.
U.S. Pat. No. 2,441,063 describes salts of alkylolamine boric esters. Generally, the salts are prepared by reacting an alkylolamine and a borating agent to form a boric ester of the amine which is then reacted with a carboxylic acid.
Mixtures of salts of monocarboxylic acids and amines with boric acid and amine are described in U.S. Pat. No. 2,999,064. Such salts are reported to be useful in aqueous cutting fluids as corrosion inhibitors.
In U.S. Pat. No. 3,282,955, reaction products of acylated nitrogen intermediates with a boron compound are described. The acylated nitrogen intermediates are formed by the reaction of a hydrocarbon substituted succinic acid and a hydroxy amine. The products are useful as additives in lubricating oils.